The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to structures for a field-effect transistor and methods of forming a structure for a field-effect transistor.
Device structures for a field-effect transistor generally include a source, a drain, and a gate electrode configured to switch carrier flow in a channel formed in a semiconductor body arranged between the source and drain. The semiconductor body and channel of a planar field-effect transistor are arranged beneath the top surface of a substrate on which the gate electrode is supported. When a control voltage exceeding a designated threshold voltage is applied to the gate electrode, the flow of carriers in the channel produces a device output current.
A fin-type field-effect transistor is a type of non-planar device structure that may be more densely packed in an integrated circuit than planar field-effect transistors. A fin-type field-effect transistor may include a fin, a source and a drain, and a gate electrode that wraps around a channel region located in the fin between the source and the drain. The wrapped arrangement between the gate structure and fin may improve control over the channel and reduce the leakage current when the fin-type field-effect transistor is in its ‘Off’ state in comparison with a planar transistor. This, in turn, may enable the use of lower threshold voltages than in planar transistors, and may result in improved performance and lowered power consumption.
Nanosheet field-effect transistors have been developed as a type of non-planar field-effect transistor that may permit additional increases in packing density in an integrated circuit. The body of a nanosheet field-effect transistor includes multiple nanosheet channel layers that are arranged in a layer stack. The nanosheet channel layers are initially arranged in a layer stack with sacrificial layers containing a material (e.g., silicon-germanium) that can be etched selectively to the material (e.g., silicon) constituting the nanosheet channel layers. The sacrificial layers are etched and removed in order to release the nanosheet channel layers and to provide spaces for the formation of a gate stack. Sections of the gate stack may surround all sides of the individual nanosheet channel layers in a gate-all-around arrangement. Similarly, nanowires may be substituted for nanosheets to form nanowire field-effect transistors.
Improved structures for a field-effect transistor and methods of forming a structure for a field-effect transistor are needed.